RESUMEN
Infraorbital nerve (ION) transection in neonatal rats leads to disruption of whisker-specific neural patterns (barrelettes), conversion of functional synapses into silent synapses, and reactive gliosis in the brain stem trigeminal principal nucleus (PrV). Here we tested the hypothesis that neonatal peripheral nerve crush injuries permit better functional recovery of associated central nervous system (CNS) synaptic circuitry compared with nerve transection. We developed an in vitro whisker pad-trigeminal ganglion (TG)-brain stem preparation in neonatal rats and tested functional recovery in the PrV following ION crush. Intracellular recordings revealed that 68% of TG cells innervate the whisker pad. We used the proportion of whisker pad-innervating TG cells as an index of ION function. The ION function was blocked by â¼64%, immediately after mechanical crush, then it recovered beginning after 3 days postinjury and was complete by 7 days. We used this reversible nerve-injury model to study peripheral nerve injury-induced CNS synaptic plasticity. In the PrV, the incidence of silent synapses increased to â¼3.5 times of control value by 2-3 days postinjury and decreased to control levels by 5-7 days postinjury. Peripheral nerve injury-induced reaction of astrocytes and microglia in the PrV was also reversible. Neonatal ION crush disrupted barrelette formation, and functional recovery was not accompanied by de novo barrelette formation, most likely due to occurrence of recovery postcritical period (P3) for pattern formation. Our results suggest that nerve crush is more permissive for successful regeneration and reconnection (collectively referred to as "recovery" here) of the sensory inputs between the periphery and the brain stem.
Asunto(s)
Nervio Maxilar/lesiones , Plasticidad Neuronal/fisiología , Neuronas/fisiología , Traumatismos de los Nervios Periféricos/fisiopatología , Recuperación de la Función/fisiología , Núcleos del Trigémino/crecimiento & desarrollo , Núcleos del Trigémino/fisiopatología , Animales , Animales Recién Nacidos , Nervio Maxilar/patología , Nervio Maxilar/fisiopatología , Nervio Maxilar/cirugía , Compresión Nerviosa , Neuroglía/fisiología , Traumatismos de los Nervios Periféricos/patología , Ratas , Ratas Sprague-Dawley , Vibrisas/crecimiento & desarrollo , Vibrisas/inervaciónRESUMEN
Ascending somatosensory pathways are crossed pathways representing each side of the body in the contralateral neocortex. The principal sensory nucleus of the trigeminal nerve (PrV) relays the facial sensations to the contralateral somatosensory cortex via the ventrobasal thalamus. In the companion article (Kivrak and Erzurumlu [2012] J. Comp. Neurol. 12-0013) we described the normal development of the trigeminal lemniscal pathway in the mouse. In this study we investigated the role of midline axon navigation signals, the netrin and slit proteins. In situ hybridization assays revealed that both netrin and slit mRNAs are expressed along the midline facing the PrV axons and their receptors are expressed in developing PrV neurons. In wild-type mouse embryos, PrV axons cross the midline and take a sharp rostral turn heading toward the contralateral thalamus. Examination of trigeminal lemniscal axons in dcc knockout mice revealed absence of midline crossing between E11 and E15. However, a few axons crossed the midline at E17 and reached the contralateral thalamus, resulting in a bilateral PrV lemniscal pathway at P0. We also found that slit1, -2 or -3 single or double knockout mice have impaired development of the trigeminal-lemniscal pathway. These include axon stalling along the midline, running within the midline, and recrossing of axons back to the site of origin. Collectively, our studies indicate a cooperative role for netrin and slit proteins in midline attraction and crossing behavior of the ascending facial somatosensory projections during development.
Asunto(s)
Factores de Crecimiento Nervioso/fisiología , Proteínas del Tejido Nervioso/fisiología , Vías Nerviosas/fisiología , Transducción de Señal/fisiología , Tálamo/fisiología , Núcleos del Trigémino/fisiología , Proteínas Supresoras de Tumor/fisiología , Animales , Axones/fisiología , Carbocianinas , Receptor DCC , Femenino , Regulación del Desarrollo de la Expresión Génica/fisiología , Hibridación in Situ , Péptidos y Proteínas de Señalización Intercelular/fisiología , Proteínas de la Membrana/fisiología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Netrina-1 , Vías Nerviosas/crecimiento & desarrollo , Embarazo , Sondas ARN , Receptores de Superficie Celular/biosíntesis , Receptores de Superficie Celular/genética , Receptores Inmunológicos/fisiología , Rombencéfalo/metabolismo , Rombencéfalo/fisiología , Núcleos del Trigémino/crecimiento & desarrollo , Proteínas Supresoras de Tumor/biosíntesis , Proteínas Supresoras de Tumor/genética , Proteínas RoundaboutRESUMEN
The principal sensory (PrV) nucleus-based trigeminal lemniscus conveys whisker-specific neural patterns to the ventroposteromedial (VPM) nucleus of the thalamus and subsequently to the primary somatosensory cortex. Here we examined the perinatal development of this pathway with carbocyanine dye labeling in embryonic and early postnatal mouse brains. We developed a novel preparation in which the embryonic hindbrain and the diencephalon are flattened out, allowing a birds-eye view of the PrV lemniscus in its entirety. For postnatal brains we used another novel approach by sectioning the brain along an empirically determined oblique horizontal angle, again preserving the trigeminothalamic pathway. PrV neurons are born along the hindbrain ventricular zone and migrate radially for a short distance to coalesce into a nucleus adjacent to the ascending trigeminal tract. During migration of the spindle-shaped cell bodies, slender axonal processes grow along the opposite direction towards the floor plate. As early as embryonic day (E) 11, pioneering axons tipped with large growth cones cross the ventral midline and immediately make a right angle turn. By E13 many PrV axons form fascicles crossing the midline and follow a rostral course. PrV axons reach the midbrain by E15 and the thalamus by E17. While the target recognition and invasion occurs prenatally, organization of PrV axon terminals into whisker-specific rows and patches takes place during the first 4 postnatal (P) days. Initially diffuse and exuberant projections in the VPM at P1 coalesce into row and whisker specific terminal zones by P4.
Asunto(s)
Núcleos del Trigémino/embriología , Núcleos del Trigémino/crecimiento & desarrollo , Animales , Carbocianinas , Diferenciación Celular , Movimiento Celular , Femenino , Procesamiento de Imagen Asistido por Computador , Inmunohistoquímica , Ratones , Ratones Endogámicos C57BL , Vías Nerviosas/citología , Vías Nerviosas/embriología , Embarazo , Terminales Presinápticos/fisiología , Tálamo/anatomía & histología , Tálamo/crecimiento & desarrollo , Proteína 2 de Transporte Vesicular de Glutamato/metabolismoRESUMEN
Unlike other primary sensory neurons, the neurons in the mesencephalic trigeminal nucleus (Vmes) receive most of their synaptic input onto their somata. Detailed description of the synaptic boutons onto Vmes neurons is crucial for understanding the synaptic input onto these neurons and their role in the motor control of masticatory muscles. For this, we investigated the distribution of γ-aminobutyric acid (GABA)-, glycine-, and glutamate-immunopositive (+) boutons on Vmes neurons and their ultrastructural parameters that relate to transmitter release: Vmes neurons that innervate masseteric muscle spindles were identified by labeling with horseradish peroxidase injected into the muscle, and immunogold staining and quantitative ultrastructural analysis of synapses onto these neurons were performed in adult rats and during postnatal development. The bouton volume, mitochondrial volume, and active zone area of the boutons contacting labeled somata (axosomatic synapses) were similar to those of boutons forming axoaxonic synapses with Vmes neurons but smaller than those of boutons forming axodendritic or axosomatic synapses with most other neurons. GABA+ , glycine+ , and glutamate+ boutons constituted a large majority (83%) of all boutons on labeled somata. A considerable fraction of boutons (28%) was glycine(+) , and all glycine+ boutons were also GABA+ . Bouton size remained unchanged during postnatal development. These findings suggest that the excitability of Vmes neurons is determined to a great extent by GABA, glycine, and glutamate and that the relatively lower synaptic strength of axosomatic synapses may reflect the role of the Vmes neurons in modulating orofacial motor function.
Asunto(s)
Músculos Masticadores/inervación , Músculos Masticadores/ultraestructura , Husos Musculares/inervación , Husos Musculares/ultraestructura , Neurotransmisores/fisiología , Terminales Presinápticos/ultraestructura , Núcleos del Trigémino/ultraestructura , Animales , Animales Recién Nacidos , Ácido Glutámico/fisiología , Glicina/fisiología , Masculino , Músculos Masticadores/crecimiento & desarrollo , Neuronas Motoras/metabolismo , Neuronas Motoras/ultraestructura , Husos Musculares/crecimiento & desarrollo , Terminales Presinápticos/metabolismo , Ratas , Ratas Sprague-Dawley , Núcleos del Trigémino/crecimiento & desarrollo , Núcleos del Trigémino/metabolismo , Ácido gamma-Aminobutírico/fisiologíaRESUMEN
Inhibitory and excitatory synaptic inputs onto trigeminal motoneurons play an important role in coordinating jaw movements. Previously, we reported that the phenotype of the inhibitory boutons apposing the somata of jaw-closing (JC) motoneurons changes from γ-aminobutyric acid (GABA)-positive (GABA+) to predominantly glycine-positive (Gly+) during development. In the present study, we investigated the development of inhibitory and excitatory boutons apposing antagonistic jaw-opening (JO) motoneurons (anterior digastric motoneurons) at postnatal day 2 (P2), P11, and P31 in the rat. JO motoneurons were retrogradely labeled with horseradish peroxidase. Postembedding immunogold staining with antisera against GABA, Gly, and glutamate (Glut) was performed and followed by quantitative ultrastructural analysis. The size of both small and large JO motoneurons increased during development. The number of excitatory (Glut+) and inhibitory (GABA+, Gly+, and GABA+/Gly+) boutons per JO motoneuron increased significantly from P2 to P11 and then remained unchanged until P31. The time course of inhibitory synapse formation differed between JO and JC motoneurons, whereas that of excitatory synapse formation was similar between the two neuronal populations. The fraction of GABA+ boutons decreased by 86% and the fraction of GABA+/Gly+ boutons increased by 200% from P11 to P31, suggesting a switch from GABA+ to GABA+/Gly+ phenotype. The fraction of Gly+ boutons remained unchanged. These results indicate that inhibitory synapses onto somata of JO motoneurons exhibit a developmental pattern distinct from that of synapses onto JC motoneurons, which may reflect distinctive maturation of oral motor system.
Asunto(s)
Ácido Glutámico/biosíntesis , Glicina/biosíntesis , Mandíbula/metabolismo , Músculos Masticadores/inervación , Neuronas Motoras/metabolismo , Inhibición Neural/fisiología , Neurotransmisores/biosíntesis , Ácido gamma-Aminobutírico/biosíntesis , Animales , Animales Recién Nacidos , Masculino , Mandíbula/citología , Masticación/fisiología , Músculos Masticadores/fisiología , Neuronas Motoras/citología , Neuronas Motoras/fisiología , Neurogénesis/fisiología , Terminales Presinápticos/metabolismo , Ratas , Ratas Sprague-Dawley , Núcleos del Trigémino/citología , Núcleos del Trigémino/crecimiento & desarrolloRESUMEN
N-methyl-D-aspartate receptors (NMDARs) play a major role in various forms of developmental and adult synaptic plasticity (Lopez de Armentia M, Sah P (2003) J Neurosci 23:6876-6883). Activity-dependent shifts in NR2 subunits of the NMDARs have been proposed to be the molecular basis of critical period plasticity. Several supporting examples have been reported; however it is not clear whether the relationship between NMDAR subunit changes and neural plasticity are correlative or causal, nor whether such a relationship is universal across all sensory pathways with developmental plasticity. In the present study, we used voltage-clamp recording techniques to investigate whether subunit composition of NMDARs changes during development and after neonatal denervation in the principal sensory nucleus (PrV) of the trigeminal nerve. Relative AMPA receptor contribution to synaptic transmission increased linearly by the second postnatal week in the normal PrV. Denervation by peripheral nerve damage did not alter this process. We took the weighted decay time constant (τw) of NMDAR-mediated EPSCs as an index for NMDAR subunit composition. The τw measurement and Western blot analysis revealed that NMDARs contained both NR2A and NR2B subunits. The NR2A/NR2B ratio did not change during postnatal development or after neonatal denervation. Thus, critical period plasticity-related pattern formation in the PrV does not depend on changes in subunit composition of NMDARs. The mechanism underlying developmental synaptic plasticity in the PrV differs from those in higher trigeminal centers and other brain structures.
Asunto(s)
Desnervación/métodos , Receptores de N-Metil-D-Aspartato/metabolismo , Núcleos del Trigémino/crecimiento & desarrollo , Núcleos del Trigémino/metabolismo , Animales , Animales Recién Nacidos , Potenciales Postsinápticos Excitadores/fisiología , Plasticidad Neuronal/fisiología , Neuronas/metabolismo , Neuronas/fisiología , Técnicas de Placa-Clamp/métodos , Nervios Periféricos/cirugía , Ratas , Ratas Sprague-Dawley , Receptores AMPA/metabolismo , Receptores de N-Metil-D-Aspartato/fisiología , Transmisión Sináptica/fisiologíaRESUMEN
The excitatory synapses on the jaw-closing (JC) motoneurons mediate the neuronal input that ensures smooth and rhythmic movements of the jaw. Recently, we have shown that the neurotransmitter phenotype of the inhibitory boutons onto JC motoneurons shifts from GABA to glycine, and new inhibitory synapses onto JC motoneurons are continuously formed during postnatal development (Paik et al. [2007] J. Comp. Neurol. 503:779789). To test whether the developmental pattern of the excitatory synapses onto JC motoneurons differs from that of the inhibitory synapses, we studied the distribution of glutamate-immunopositive boutons onto the rat JC motoneurons during postnatal development by using a combination of retrograde labeling with horseradish peroxidase (HRP), postembedding immunogold staining, and quantitative ultrastructural analysis. The analysis of 175, 281, and 465 boutons contacting somata of JC motoneurons at postnatal days P2, P11, and P31, respectively, revealed that the number of glutamate-immunopositive (Glut(+)) boutons increased by 2.6 times from P2 to P11 and showed no significant change after that, whereas the length of apposition of these boutons increased continuously from P2 to P31, suggesting that the time course for the development of Glut(+) boutons differed from that for Glut(-) boutons, most of which were immunopositive for GABA and/or glycine. Our findings indicate that excitatory and inhibitory synapses onto JC motoneurons exhibit distinctly different developmental patterns that may be closely related to the maturation of the masticatory system.
Asunto(s)
Maxilares/inervación , Neuronas Motoras/ultraestructura , Neurogénesis , Terminales Presinápticos/ultraestructura , Núcleos del Trigémino/ultraestructura , Animales , Ácido Glutámico/metabolismo , Inmunohistoquímica , Maxilares/ultraestructura , Masculino , Microscopía Electrónica de Transmisión , Neuronas Motoras/metabolismo , Terminales Presinápticos/metabolismo , Ratas , Ratas Sprague-Dawley , Núcleos del Trigémino/crecimiento & desarrollo , Núcleos del Trigémino/metabolismoRESUMEN
The trigeminal mesencephalic nucleus (Vmes) is known to include primary afferent neurons of jaw muscle spindles (MS neurons) and periodontal ligament receptors (PL neurons). The aim of this study was to clarify the postnatal development of Vmes neurons by comparing MS neurons with PL neurons using horseradish peroxidase labeling. We measured somal diameter and somal shape of MS and PL neurons in rats from postnatal day (P)7 to P70. No significant changes were seen between postnatal day P7 and P70 in somal diameter or somal shape of MS neurons. Conversely, PL neurons showed a larger somal diameter at P7 than at P14, and in terms of somal profile, multipolar neurons comprised 0% at P7, but 4.8% at P14 and 16.9% at P70. These findings suggest that PL neurons develop with the eruption of teeth, taking into account the fact that tooth eruption occurs from around P14 in rats. Conversely, the lack of postnatal changes in MS neurons is due to the fact that these neurons have been active since the embryonic period, as swallowing starts in utero.
Asunto(s)
Mesencéfalo/citología , Husos Musculares/citología , Neuronas/citología , Ligamento Periodontal/inervación , Periodoncio/inervación , Núcleos del Trigémino/citología , Animales , Forma de la Célula , Tamaño de la Célula , Femenino , Masculino , Mesencéfalo/crecimiento & desarrollo , Husos Musculares/crecimiento & desarrollo , Ligamento Periodontal/crecimiento & desarrollo , Periodoncio/crecimiento & desarrollo , Ratas , Ratas Wistar , Núcleos del Trigémino/crecimiento & desarrolloRESUMEN
We previously reported that electrical stimulation of the reticular formation dorsal to the facial nucleus (RdVII) elicited excitatory masseter responses at short latencies and that RdVII neurons were antidromically activated by stimulation of the trigeminal motor nucleus (MoV), suggesting that excitatory premotor neurons targeting the MoV are likely located in the RdVII. We thus examined the properties of synaptic transmission from the RdVII to jaw-closing and jaw-opening motoneurons in horizontal brainstem preparations from developing rats using voltage-sensitive dye, patch-clamp recordings and laser photostimulation. Electrical stimulation of the RdVII evoked optical responses in the MoV. Combined bath application of the non-N-methyl-d-aspartate (non-NMDA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and the NMDA receptor antagonist DL-2-amino-5-phosphonopentanoic acid (APV) reduced these optical responses, and addition of the glycine receptor antagonist strychnine and the GABA(A) receptor antagonist bicuculline further reduced the remaining responses. Electrical stimulation of the RdVII evoked postsynaptic currents (PSCs) in all 19 masseter motoneurons tested in postnatal day (P)1-4 rats, and application of CNQX and the NMDA receptor antagonist (+/-)-3(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) reduced the PSC amplitudes by more than 50%. In the presence of CNQX and CPP, the GABA(A) receptor antagonist SR95531 further reduced PSC amplitude, and addition of strychnine abolished the remaining PSCs. Photostimulation of the RdVII with caged glutamate also evoked PSCs in masseter motoneurons of P3-4 rats. In P8-11 rats, electrical stimulation of the RdVII also evoked PSCs in all 14 masseter motoneurons tested, and the effects of the antagonists on the PSCs were similar to those in P1-4 rats. On the other hand, RdVII stimulation evoked PSCs in only three of 16 digastric motoneurons tested. These results suggest that both neonatal and juvenile jaw-closing motoneurons receive strong synaptic inputs from the RdVII through activation of glutamate, glycine and GABA(A) receptors, whereas inputs from the RdVII to jaw-opening motoneurons seem to be weak.
Asunto(s)
Neuronas Motoras/fisiología , Formación Reticular/fisiología , Transmisión Sináptica , Núcleos del Trigémino/fisiología , Animales , Animales Recién Nacidos , Estimulación Eléctrica , Técnicas In Vitro , Músculo Masetero/crecimiento & desarrollo , Músculo Masetero/inervación , Técnicas de Placa-Clamp , Estimulación Luminosa , Ratas , Ratas Wistar , Receptores de GABA-A/fisiología , Receptores de Glutamato/fisiología , Receptores de Glicina/fisiología , Formación Reticular/crecimiento & desarrollo , Potenciales Sinápticos , Núcleos del Trigémino/citología , Núcleos del Trigémino/crecimiento & desarrolloRESUMEN
In vertebrates, sensory specializations are usually correlated with increases in the brain areas associated with that specialization. This correlation is called the 'principle of proper mass' whereby the size of a neural structure is a reflection of the complexity of the behavior that it subserves. In recent years, several comparative studies have revealed examples of this principle in the visual and auditory system of birds, but somatosensory specializations have largely been ignored. Many species rely heavily on tactile information during feeding. Input from the beak, tongue and face, conveyed via the trigeminal, facial, glossopharyngeal and hypoglossal nerves, is first processed in the brain by the principal sensory nucleus of the trigeminal nerve (PrV) in the brainstem. Previous studies report that PrV is enlarged in some species that rely heavily on tactile input when feeding, but no extensive comparative studies have been performed. In this study, we assessed the volume of PrV in 73 species of birds to present a detailed analysis of the relative size variation of PrV using both conventional and phylogenetically based statistics. Overall, our results indicate that three distinct groups of birds have a hypertrophied PrV: waterfowl (Anseriformes), beak-probing shorebirds (Charadriiformes), and parrots (Psittaciformes). These three groups have different sensory requirements from the orofacial region. For example, beak-probing shorebirds use pressure information from the tip of the beak to find buried prey in soft substrates, whereas waterfowl, especially filter-feeding ducks, use information from the beak, palate, and tongue when feeding. Parrots likely require increased sensitivity in the tongue to manipulate food items. Thus, despite all sharing an enlarged PrV and feeding behaviors dependent on tactile input, each group has different requirements that have led to the independent evolution of a large PrV.
Asunto(s)
Evolución Biológica , Aves/fisiología , Núcleos del Trigémino/fisiología , Animales , Anseriformes , Encéfalo/anatomía & histología , Columbiformes , Falconiformes , Conducta Alimentaria , Galliformes , Ganglios Sensoriales/anatomía & histología , Ganglios Sensoriales/fisiología , Bulbo Olfatorio/anatomía & histología , Bulbo Olfatorio/fisiología , Passeriformes , Filogenia , Psittaciformes , Núcleos del Trigémino/anatomía & histología , Núcleos del Trigémino/crecimiento & desarrolloRESUMEN
Our previous study showed that developmental changes to serotonin and substance P coexist in the trigeminal motor nucleus (Vmo), dorsolateral subnucleus (Vmo.dl), ventromedial subnucleus (Vmo.vm) and the area within 300 microm surrounding Vmo (SVmo). This occurred in rats from embryonic day (E)19 to postnatal day (P)70, with density of these terminals peaking at P7 in these three areas. The present study examined postnatal development of serotonergic 1A receptor (5HT1A receptor) and substance P receptor (NK1 receptor) expression in Vmo and SVmo in rats from E19 to P70. No significant changes in percentages of 5HT1A and NK1 receptor-expressing cells were seen between E19 and P70 by immunohistochemical study or in situ hybridization. In a real-time PCR study, quantities of 5HT1A and NK1 receptor expression peaked at P7, indicating that expression of these receptors was maximized in each neuronal cell body in the Vmo and SVmo at P7. This result corresponds with postnatal changes in serotonin/substance P-coexisting terminals found in our previous study. Furthermore, 5HT1A and NK1 receptors displayed very similar patterns of expression, which may support the hypothesis that potentiation of serotonin and substance P are involved in excitability regulating trigeminal motor functions, including mastication and breathing.
Asunto(s)
Receptores de Neuroquinina-1/metabolismo , Receptores de Serotonina/metabolismo , Núcleos del Trigémino/crecimiento & desarrollo , Núcleos del Trigémino/metabolismo , Animales , Animales Recién Nacidos , Femenino , Inmunohistoquímica , Hibridación in Situ , Masculino , ARN Mensajero/biosíntesis , ARN Mensajero/genética , Ratas , Ratas Wistar , Receptor de Serotonina 5-HT1A/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
The mesencephalic trigeminal nucleus (Me5) innervates muscle spindles and is responsible for receiving and transmitting proprioception from the oro-facial region. Molecular mechanisms underlying the development of the Me5 are poorly understood. Evidence is provided here that transcription factor Drg11 is required for Me5 development. Drg11 was expressed in the Me5 cells of the embryonic and early postnatal mouse brains, and the Me5 cells were absent in Drg11-/- mice at birth. The absence of the Me5 cells in Drg11-/- mice appeared to be caused by increased cell death in the Me5 during embryonic development. In postnatal Drg11-/- mice, Me5 cell innervation of masseter muscle spindles was undetectable, while robust trigeminal motoneuron innervation of masseter muscle fibers was detected. The postnatal body weight of Drg11-/- mice was notably less than that of wild-type mice, and this might result, in part, from disruption of the oro-facial proprioceptive afferent pathway. Taken together, our results demonstrate an essential role for Drg11 in the development of the Me5.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Factores de Transcripción/metabolismo , Núcleos del Trigémino , Factores de Edad , Animales , Animales Recién Nacidos , Peso Corporal/genética , Embrión de Mamíferos , Regulación del Desarrollo de la Expresión Génica/genética , Proteínas de Homeodominio/genética , Hibridación in Situ/métodos , Etiquetado Corte-Fin in Situ/métodos , Ratones , Ratones Noqueados , Proteínas del Tejido Nervioso/genética , Parvalbúminas/metabolismo , Factores de Transcripción/genética , Núcleos del Trigémino/embriología , Núcleos del Trigémino/crecimiento & desarrollo , Núcleos del Trigémino/metabolismoRESUMEN
The noradrenergic (NA) innervation in the trigeminal motor nucleus (Vmot) of postnatal and adult rats was examined by light and electron microscopic immunocytochemistry using antibodies against dopamine-beta-hydroxylase or tyrosine hydroxylase. NA fibers were identified in the Vmot as early as the day of birth (postnatal day 0; P0). A continuous increase in the density of labeled fibers was observed during development up to P20, with a slight decrease at P30 and in the adult. Electron microscopic analysis of serial ultrathin sections revealed that, at P5, nearly half (46%) of the examined NA terminals made synaptic contact with other neuronal elements with membrane specializations. The percentage of examined NA varicosities engaged in synaptic contacts increased at P15 (74%), then decreased in the adult (64%). At all developmental ages, the majority of contacts made by these boutons were symmetrical, the postsynaptic elements being mainly dendrites and occasionally somata. Interestingly, some of the NA terminals made axo-axon contacts with other unidentified boutons. These results show that, although the density of NA fibers increases during postnatal development, functional NA boutons are present in the Vmot at early postnatal ages. Some of these fibers might exert their effects via nonsynaptic release of noradrenaline, the so-called volume transmission, but, in the main, they form conventional synaptic contacts with dendrites, somata, and other axonal terminals in the Vmot. These results are consistent with previous electrophysiological studies that propose an important role for the NA system in modulating mastication.
Asunto(s)
Norepinefrina/metabolismo , Terminales Presinápticos/metabolismo , Terminales Presinápticos/ultraestructura , Núcleos del Trigémino/citología , Núcleos del Trigémino/crecimiento & desarrollo , Envejecimiento/metabolismo , Envejecimiento/patología , Animales , Axones/metabolismo , Axones/ultraestructura , Recuento de Células , Dopamina beta-Hidroxilasa/metabolismo , Femenino , Maxilares/inervación , Maxilares/fisiología , Masculino , Masticación/fisiología , Ratas , Ratas Wistar , Núcleos del Trigémino/enzimología , Tirosina 3-Monooxigenasa/metabolismoRESUMEN
Naturally occurring cell death is a universal feature of developing nervous systems that plays an essential role in determining adult brain function. Yet little is known about the decisions that select a subset of CNS neurons for survival and cause others to die. We report that postnatal day 0 NMDA receptor subunit 1 (NMDAR1) knockout mice display an approximately 2-fold increase in cell death in the brainstem trigeminal complex (BSTC), including all four nuclei that receive somatosensory inputs from the face (principalis, oralis, interpolaris, and caudalis). Treatment with the NMDA receptor antagonist dizocilpine maleate (MK-801) for 24 h before birth also caused an increase in cell death that reached statistical significance in two of the four nuclei (oralis and interpolaris). The neonatal sensitivity to NMDA receptor hypofunction in the BSTC, and in its main thalamic target, the ventrobasal nucleus (VB), coincides with the peak of naturally occurring cell death and trigeminothalamic synaptogenesis. At embryonic day 17.5, before the onset of these events, NMDAR1 knockout does not affect cell survival in either the BSTC or the VB. Immunostaining for active caspase-3 and the neuronal marker Hu specifically confirms the presence of dying neurons in the BSTC and the VB of NMDAR1 knockout neonates. Finally, genetic deletion of Bax rescues these structures from the requirement for NMDA receptors to limit naturally occurring cell death. Taken together, the results indicate that NMDA receptors play a survival role for somatosensory relay neurons during synaptogenesis by inhibiting Bax-dependent developmental cell death.
Asunto(s)
Receptores de N-Metil-D-Aspartato/fisiología , Corteza Somatosensorial/citología , Corteza Somatosensorial/fisiología , Núcleos del Trigémino/citología , Núcleos del Trigémino/fisiología , Proteína X Asociada a bcl-2/fisiología , Animales , Apoptosis/fisiología , Secuencia de Bases , Supervivencia Celular/fisiología , Cartilla de ADN/genética , Maleato de Dizocilpina/farmacología , Femenino , Ratones , Ratones Noqueados , Embarazo , Receptores de N-Metil-D-Aspartato/antagonistas & inhibidores , Receptores de N-Metil-D-Aspartato/deficiencia , Receptores de N-Metil-D-Aspartato/genética , Corteza Somatosensorial/efectos de los fármacos , Corteza Somatosensorial/crecimiento & desarrollo , Núcleos del Trigémino/efectos de los fármacos , Núcleos del Trigémino/crecimiento & desarrollo , Proteína X Asociada a bcl-2/deficiencia , Proteína X Asociada a bcl-2/genéticaRESUMEN
Post-weaning mice fed exclusively milk display low-frequency exploratory behavior [Ishii, T., Itou, T., and Nishimura, M. (2005) Life Sci. 78, 174-179] compared to mice fed a food pellet diet. This low-frequency exploratory behavior switched to high-frequency exploration after a switch from exclusively milk formula to a food pellet diet. Acquisition of the high-frequency exploratory behavior was irreversible. Recently, we demonstrated that the mesencephalic trigeminal nucleus (Me5) is involved in the control of feeding and exploratory behavior in mice without modulating the emotional state [Ishii, T., Furuoka, H., Itou, T., Kitamura, N., and Nishimura, M. (2005) Brain Res. 1048, 80-86]. We therefore investigated whether the Me5 is involved in acquisition of high-frequency exploratory behavior induced by the switch in diet from an exclusively milk formula to food pellets. Mouse feeding and exploratory behaviors were analyzed using a food search compulsion apparatus, which was designed to distinguish between the two behaviors under standard living conditions. Immunohistochemical analysis of immediate early genes indicated that the Me5, which receives signals from oral proprioceptors, is transiently activated after the diet change. The change from low-frequency to high-frequency exploratory behavior was prevented in milk-fed mice by bilateral lesion of the Me5. These results suggest that the Me5 is activated by signals associated with mastication-induced proprioception and contributes to the acquisition of active exploratory behavior.
Asunto(s)
Ingestión de Alimentos/fisiología , Conducta Exploratoria/fisiología , Alimentos Formulados , Mesencéfalo/crecimiento & desarrollo , Núcleos del Trigémino/crecimiento & desarrollo , Destete , Vías Aferentes/anatomía & histología , Vías Aferentes/crecimiento & desarrollo , Animales , Conducta Animal/fisiología , Peso Corporal/fisiología , Desnervación , Alimentos , Regulación de la Expresión Génica/fisiología , Inmunohistoquímica , Masculino , Masticación/fisiología , Mesencéfalo/anatomía & histología , Mesencéfalo/lesiones , Ratones , Leche/metabolismo , Boca/inervación , Boca/fisiología , Proteínas Proto-Oncogénicas c-fos/metabolismo , Factores de Tiempo , Nervio Trigémino/anatomía & histología , Nervio Trigémino/crecimiento & desarrollo , Núcleos del Trigémino/anatomía & histología , Núcleos del Trigémino/lesionesRESUMEN
The major neuronal components of the trigeminal mesencephalic nucleus (Vmes) are primary afferent neurons that convey proprioceptive information from the cranioorofacial regions. In the present study, we examined expression of vesicular glutamate transporters (VGLUTs), VGLUT1 and VGLUT2, in the primary afferent neurons of the Vmes (Vmes neurons) in neonatal and adult rats. VGLUT1 immunoreactivity was detected in the cell bodies of Vmes neurons in neonatal rats younger than 11 days old, but not in older rats. However, in situ hybridization signals for VGLUT1 mRNA were detected in both neonatal and adult rats. No VGLUT2 immunoreactivity was detected in Vmes neurons of neonatal or adult rats. VGLUT1 immunoreactivity was also seen in the peripheral sensory endings on the equatorial regions of intrafusal fibers of muscle spindles in the masseter muscles in both neonatal and adult rats. In adult rats injected with cholera toxin B subunit (CTb) into the masseter nerve, central axon terminals of Vmes neurons were identified on masseter motoneurons within the trigeminal motor nucleus (Vm) by transganglionically and retrogradely transported CTb. VGLUT1-immunopositive axon terminals in close apposition to CTb-labeled Vm motoneurons were also detected by dual-immunofluorescence histochemistry for VGLUT1/CTb. Electron microscopy after dual immunolabeling for VGLUT1/CTb by the VGLUT1/immunoperoxidase and CTb/immunogold-silver methods further revealed synaptic contact of VGLUT1- and CTb-immunopositive axon terminals upon CTb-labeled neuronal profiles within the Vm. These data indicate that VGLUT1 is expressed in both the central axon terminals and the peripheral sensory endings of Vmes neurons, although no VGLUT1 immunoreactivity was detectable in the cell bodies of Vmes neurons in adult rats.
Asunto(s)
Ácido Glutámico/metabolismo , Neuronas Aferentes/metabolismo , Terminales Presinápticos/metabolismo , Células Receptoras Sensoriales/metabolismo , Núcleos del Trigémino/metabolismo , Proteína 1 de Transporte Vesicular de Glutamato/metabolismo , Envejecimiento/fisiología , Animales , Toxina del Cólera , Inmunohistoquímica , Músculo Masetero/crecimiento & desarrollo , Músculo Masetero/inervación , Músculo Masetero/ultraestructura , Microscopía Electrónica de Transmisión , Neuronas Motoras/metabolismo , Neuronas Motoras/ultraestructura , Husos Musculares/crecimiento & desarrollo , Husos Musculares/ultraestructura , Neuronas Aferentes/ultraestructura , Terminales Presinápticos/ultraestructura , Propiocepción/fisiología , Ratas , Ratas Sprague-Dawley , Células Receptoras Sensoriales/ultraestructura , Transmisión Sináptica/fisiología , Núcleos del Trigémino/crecimiento & desarrollo , Núcleos del Trigémino/ultraestructura , Proteína 1 de Transporte Vesicular de Glutamato/genéticaRESUMEN
To examine the contribution of whisker inputs to the initial emergence and subsequent refinement of the rodent whisking pattern we combined surgical treatments producing varying degrees of postnatal whisker deafferentation with observations and video analysis of whisking across the first month of life. Whisking emerges during the second postnatal week, preceding eye opening by a few days. In contrast to the absence of deafferentation effects in adults, whisker deafferentation in pups, if carried out between the second and third postnatal week, delays (but does not prevent) the emergence of whisker movements and disrupts the development of normal whisking kinematics and coordination. The extent of the delay varies directly with the reduction in whisker input. When regeneration of the nerve is prevented by a cyanoacrylate block emergence of the normal pattern may be delayed indefinitely. Moreover, section of the whisker motor nerve contralateral to the deafferented side, substantially potentiates the effects of the initial deafferentation. These results confirm and extend an earlier description of the development of whisking in normal rat pups (Welker, Behaviour 12:223-244, 1964), fix the time of its initial emergence more precisely at P (postnatal day) 11-13, and suggest a critical role for trigeminal afference in the development of the normal whisking pattern. They are discussed in relation to the development of pattern generating mechanisms in the rodent whisker system.
Asunto(s)
Ganglio del Trigémino/fisiología , Núcleos del Trigémino/fisiología , Vibrisas/inervación , Vibrisas/fisiología , Factores de Edad , Animales , Conducta Animal/fisiología , Desnervación , Femenino , Masculino , Neuronas Motoras/fisiología , Movimiento/fisiología , Regeneración Nerviosa/fisiología , Neuronas Aferentes/fisiología , Estimulación Física , Ratas , Ratas Long-Evans , Corteza Somatosensorial/citología , Corteza Somatosensorial/crecimiento & desarrollo , Corteza Somatosensorial/fisiología , Ganglio del Trigémino/citología , Ganglio del Trigémino/crecimiento & desarrollo , Núcleos del Trigémino/citología , Núcleos del Trigémino/crecimiento & desarrolloRESUMEN
The N-methyl-d-aspartate (NMDA) receptor plays an important role in the generation of rhythmical oral motor activities. To compliment our previous studies, we examined the developmental regulation of NR3A and NR3B expression in trigeminal motoneurons (Mo5) and mesencephalic trigeminal neurons (Me5). NR3A-immunoreactive neurons were observed at all ages in both nuclei, decreasing in Mo5 and caudal Me5 after P14, and increasing in rostral Me5. NR3B protein expression only emerged in Mo5 after P21-23. Results indicate that NR3A and NR3B expression is differentially regulated between Mo5 and Me5 coincident with the transition from suckling to chewing.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica/fisiología , Mesencéfalo/citología , Neuronas Motoras/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Núcleos del Trigémino/citología , Factores de Edad , Análisis de Varianza , Animales , Animales Recién Nacidos , Recuento de Células/métodos , Inmunohistoquímica/métodos , Mesencéfalo/crecimiento & desarrollo , Ratas , Ratas Sprague-Dawley , Receptores de N-Metil-D-Aspartato/genética , Núcleos del Trigémino/crecimiento & desarrolloRESUMEN
The occurrence of Ret and GFRalpha-1 receptors is shown by immunohistochemistry in the human trigeminal sensory system at pre-, postnatal and adult age. Receptor-labeled neurons occur in both trigeminal ganglion and mesencephalic nucleus. In adult trigeminal ganglion, about 75% of Ret- and 65% of GFRalpha-1-labeled neurons are small- and medium-sized. The proportion of Ret+ and GFRalpha-1+ trigeminal ganglion neurons in the adult is about 25 and 60%, respectively. The majority of Ret+ are double labeled for GFRalpha-1 and glial cell line-derived neurotrophic factor (GDNF). Most of the GFRalpha-1+ cells contain GDNF and about 50% of them contain Ret. Triple labeling shows many Ret+/GDNF+/GFRalpha-1+ neurons, but also a number of Ret-/GDNF+/GFRalpha-1+ and Ret+/GDNF-/GFRalpha-1+ cells. Both Ret+ and GFRalpha-1+ neuronal subpopulations overlap with that containing calcitonin gene-related peptide. Ret+ pericellular basket-like nerve fibers occur in the adult trigeminal ganglion. Centrally, immunoreactivity is restricted to the spinal nucleus pars caudalis and pars interpolaris and to the mesencephalic nucleus. In adult specimens, Ret+ nerve fibers and puncta gather in the inner substantia gelatinosa. Ret+ neurons occur in the spinal nucleus and are more frequent in newborn than in adult subjects. Central GFRalpha-1+-labeled neurons and punctate elements are sparse. These findings support the involvement of GDNF and possibly other cognate ligands in the trophism of human trigeminal primary sensory neurons from prenatal life to adulthood, indicating a selective commitment to cells devoted to protopathic and proprioceptive sensory transmission. They also support the possibility that receptor molecules other than Ret could be active in transducing the ligand signal.
Asunto(s)
Receptores del Factor Neurotrófico Derivado de la Línea Celular Glial/metabolismo , Proteínas Proto-Oncogénicas c-ret/metabolismo , Ganglio del Trigémino/metabolismo , Núcleos del Trigémino/metabolismo , Adulto , Anciano , Anciano de 80 o más Años , Péptido Relacionado con Gen de Calcitonina/metabolismo , Feto/metabolismo , Factor Neurotrófico Derivado de la Línea Celular Glial/metabolismo , Humanos , Inmunohistoquímica , Lactante , Recién Nacido , Persona de Mediana Edad , Ganglio del Trigémino/embriología , Ganglio del Trigémino/crecimiento & desarrollo , Núcleos del Trigémino/embriología , Núcleos del Trigémino/crecimiento & desarrolloRESUMEN
The development of ordered connections or "maps" within the nervous system is a common feature of sensory systems and is crucial for their normal function. NMDA receptors are known to play a key role in the formation of these maps; however, the intracellular signaling pathways that mediate the effects of glutamate are poorly understood. Here, we demonstrate that SynGAP, a synaptic Ras GTPase activating protein, is essential for the anatomical development of whisker-related patterns in the developing somatosensory pathways in rodent forebrain. Mice lacking SynGAP show only partial segregation of barreloids in the thalamus, and thalamocortical axons segregate into rows but do not form whisker-related patches. In cortex, layer 4 cells do not aggregate to form barrels. In Syngap(+/-) animals, barreloids develop normally, and thalamocortical afferents segregate in layer 4, but cell segregation is retarded. SynGAP is not necessary for the development of whisker-related patterns in the brainstem. Immunoelectron microscopy for SynGAP from layer 4 revealed a postsynaptic localization with labeling in developing postsynaptic densities (PSDs). Biochemically, SynGAP associates with the PSD in a PSD-95-independent manner, and Psd-95(-/-) animals develop normal barrels. These data demonstrate an essential role for SynGAP signaling in the activity-dependent development of whisker-related maps selectively in forebrain structures indicating that the intracellular pathways by which NMDA receptor activation mediates map formation differ between brain regions and developmental stage.